35 research outputs found
Dynamical scaling in branching models for seismicity
We propose a branching process based on a dynamical scaling hypothesis
relating time and mass. In the context of earthquake occurrence, we show that
experimental power laws in size and time distribution naturally originate
solely from this scaling hypothesis. We present a numerical protocol able to
generate a synthetic catalog with an arbitrary large number of events. The
numerical data reproduce the hierarchical organization in time and magnitude of
experimental inter-event time distribution.Comment: 3 figures to appear on Physical Review Letter
Evaluating the incompleteness magnitude using an unbiased estimate of the value
The evaluation of the value of the Gutenberg-Richter (GR) law, for a
sample composed of earthquakes, presents a systematic positive bias which is proportional to , as already observed by Ogata \& Yamashina
(1986). In this study we show how to incorporate in the bias
introduced by deviations from the GR law. More precisely we show that is proportional to the square of the variability coefficient , defined
as the ratio between {the standard deviation of the magnitude distribution and
its mean value.} When the magnitude distribution follows the GR law and
this allows us to introduce a new procedure, based on the dependence of on
, which allows us to {identify} the incompleteness magnitude as the
threshold magnitude leading to . The method is tested on synthetic
catalogs and it is applied to estimate in Southern California, Japan and
New Zealand
Subduction age and stress state control on seismicity in the NW Pacific subducting plate
Intermediate depth (70-300 km) and deep (> 300 km) earthquakes have always been puzzling Earth scientists: their occurrence is a paradox, since the ductile behavior of rocks and the high confining pressure with increasing depths would theoretically preclude brittle failure and frictional sliding. The mechanisms proposed to explain deep earthquakes, mainly depending on the subducting plate age and stress state, are generally expressed by single parameters, unsuitable to comprehensively account for differences among distinct subduction zones or within the same slab. We analyze the Kurile and Izu-Bonin intraslab seismicity and detail the Gutenberg-Richter b-value along the subducted planes, interpreting its variation in terms of stress state, analogously to what usually done for shallow earthquakes. We demonstrate that, despite the slabs different properties (e.g., lithospheric age, stress state, dehydration rate), in both cases deep earthquakes are restricted to depths characterized by equal age from subduction initiation and are driven by stress regimes affected by the persistence of the metastable olivine wedge
Unjamming dynamics: the micromechanics of a seismic fault model
The unjamming transition of granular systems is investigated in a seismic
fault model via three dimensional Molecular Dynamics simulations. A two--time
force--force correlation function, and a susceptibility related to the system
response to pressure changes, allow to characterize the stick--slip dynamics,
consisting in large slips and microslips leading to creep motion. The
correlation function unveils the micromechanical changes occurring both during
microslips and slips. The susceptibility encodes the magnitude of the incoming
microslip.Comment: See http://prl.aps.org/supplemental/PRL/v104/i23/e238001 for related
animation
How long is an aftershock sequence?
The occurrence of a mainschok is always followed by aftershocks spatially distributed within the fault area. The aftershocks rate decay with time is described by the empirical Omori law which was inferred by catalogues analysis. The sequences discrimination within catalogues is not a straightforward operation, especially for low-magnitude mainshocks. Here, we describe the rate decay of the Omori law obtained using different sequence discrimination tools and we discover that, when the background seismicity is excluded, the sequences tend to last for the temporal extension of the catalogue